Clinical Implementation of Robust Multi-isocentric Volumetric Modulated Arc Radiotherapy for Craniospinal Irradiation.

AIMS: To determine if multi-isocentric volumetric modulated arc radiotherapy for craniospinal irradiation (CSI-VMAT) can be implemented safely and accurately using robust optimisation in a commercially available treatment planning system. Our initial clinical experience is reported for the first 20 patients treated with the technique. MATERIALS AND METHODS: Patients received between 23.4 and 39.6 Gy (mode 23.4 Gy) in 13-22 fractions with CSI-VMAT. The heart mean dose was 4.2-10.3 Gy (median 5.3 Gy) for patients prescribed up to 24 Gy and 6.5-16.3 Gy (median 10.1 Gy) for patients receiving 35 Gy or more. The lung mean dose was 5.5-7.6 Gy (median 6.8 Gy) for patients prescribed up to 24 Gy and 6.9-11.1 Gy (median 10.0 Gy) for patients receiving 35 Gy or more. The robustness of the planning target volume D0.1cm3 and D99% to systematic errors in the isocentre superoinferior position of up to 5 mm was evaluated. These remained acceptable but were correlated to the length of the available beam overlap through the neck. RESULTS: As of January 2021, one patient was deceased after 508 days and one patient was lost to follow-up after completing treatment. The median follow-up was 399 days (range 175-756 days) and progression-free survival was 131 days (34-490 days). Acute toxicities at Common Terminology Criteria for Adverse Events v5.0 grade 3+ included lowered white blood cell count (16/20), decreased platelet count (8/20), nausea (5/20), vomiting (2/20), pharyngeal mucositis (1/20) and oral mucositis (1/20). Three patients developed grade 4 neutropenia or decreased white blood cell count. CONCLUSIONS: CSI-VMAT can be implemented safely and accurately using robust optimisation functions in a commercially available treatment planning system.

A dosimetric comparison between two intensity-modulated radiotherapy techniques: tomotherapy vs dynamic linear accelerator.

This manuscript describes a direct comparison between radiation treatment plans in terms of dosimetric outcomes created by two different IMRT systems: TomoTherapy HiArt and dynamic linac intensity-modulated radiotherapy (dIMRT). Three patient cases were selected (with disease in different anatomical areas): vertebral metastasis re-treatment, radical prostate therapy and an ethmoid sarcoma re-treatment. Each case presents significant and varying dosimetric difficulties with respect to avoidance of adjacent organs. The patients were each planned and treated at the Cromwell Hospital (London, UK) using the TomoTherapy HiArt system, with planning replicated at St Bartholomew's Hospital (London, UK) using Eclipse Treatment Planning System and a 6EX linac with a 120-leaf multileaf collimator (Varian Medical Systems). For both modalities, all treatment plans conformed to the stringent clinical dose constraints set. For the vertebral body re-treatment, both techniques demonstrated adequate and similar planning target volume (PTV) coverage and sparing of the spinal cord. The critical structure sparing and PTV coverage for the prostate treatment was again similar for both modalities. For re-treatment of the paediatric ethmoid sarcoma, tomotherapy was able to produce slightly better organ sparing whilst producing PTV coverage similar to linac dIMRT. The data presented in this manuscript demonstrate subtle dosimetric differences between the two techniques but no marked advantage with either system. Therefore, other factors may need to be considered when making a decision between tomotherapy and linac dIMRT.